I am very thankful to your insights, suggestions and for the effort of re-running my calculations. I will apply your suggestions in my recalculations. But I have a question sir. Would it be fine if some of my MP4 single point calculations have that keywords and some don't? That is, I'll only apply the keywords you have suggested on the molecules in which I have some problem with. I am bit worried about the energy differences that I would be obtaining, most especially since in some of my reactions, only in one molecule that I encountered this MP4 problem.